It is known that optical fibers are stronger in compression than in tension, as described in U.S. Pat. No. 5,469,520, entitled “Compression Tuned Fiber Grating,” to Morey et al. It is also known that Bragg gratings embedded in the optical fiber may be used in compression to act as a tunable filter or tunable fiber laser, as is described in U.S. Pat. No. 5,469,520, entitled “Compression Tuned Fiber Grating,” to Morey et al. and U.S. Pat. No. 5,691,999, entitled “Compression Tuned Fiber Laser,” to Ball et al., respectively, which are hereby incorporated herein by reference.
To avoid fiber buckling under compression, the technique described in the aforementioned U.S. Pat. Nos. 5,469,520 and 5,691,999 uses sliding ferrules around the fiber and grating and places the ferrules in a mechanical structure to guide, align and confine the ferrules and the fiber. However, it would be desirable to obtain a configuration that allows a fiber grating to be compressed without buckling and without sliding ferrules and without requiring such a mechanical structure.
Also, it is known to attach an optical fiber grating to within a glass tube to avoid buckling under compression for providing a wavelength-stable temperature compensated fiber Bragg grating as is described in U.S. Pat. No. 5,042,898, entitled “Incorporated Bragg Filter Temperature Compensated Optical Waveguide Device,” to Morey et al. However, such a technique exhibits creep between the fiber and the tube over time, or at high temperatures, or over large compression ranges.
It is also known that Bragg gratings in optical fibers may create unwanted coupling between the core and cladding modes of a fiber. The larger the mode field overlap between the two modes, the larger the coupling. Such coupling creates unwanted optical losses in the fiber.
It is also known that when writing Bragg gratings in optical fibers, if high power is used, the fiber may be damaged due to surface ablations on the surface of the fiber caused by the high optical power.